1. Field of the Invention
This invention relates to a system for controlling or interrupting the fuel supply in an internal combustion engine, and more particularly to a system including a pressure responsive valve which readily discriminates between an engine braking condition and an idling condition.
2. Description of the Prior Art
Hitherto, there have been proposed many attempts for interrupting fuel supply to an intake system so as to suppress generation of harmful constituents in the exhaust gases, when an internal combustion engine remains in an engine braking condition. One of these attempts is disclosed in Published Japanese Patent Application Sho No. 50-150,531. More particularly, in these attempts, a vacuum in an intake pipe downstream of a throttle valve is connected to a diaphragm chamber in a valve, so that when a vacuum thus introduced is at a level higher than a predetermined level, the fuel supply is interrupted, assuming that the engine is in an engine braking condition. The above predetermined vacuum level is set to a mean value between the maximum possible vacuum level in the intake pipe upon idling and the minimum possible vacuum level in the intake pipe, upon engine braking, i.e., a midpoint between the two vacuum levels. For instance, a vacuum level in an intake pipe in an automobile running at the sea level is 620 mmHg upon engine braking, and 500 mmHg upon idling, while a vacuum level in an intake pipe in an automobile running about 1000 meters above the sea level is 540 mmHg, upon engine braking and 450 mmHg upon idling. Thus, the aforesaid given level, at which a diaphragm is deflected, is set to a mean value between 500 mmHg and 540 mmHg, i.e., to 520 mmHg. In this case, a range or allowance to be sensed remains only .+-.20 mmHg. Accordingly, taking into consideration the possibility of that automobile running at a level higher than 1000 meters above the sea level, and manufacturing errors of diaphragms, the above allowance of .+-.20 mmHg is insufficient.